Internal combustion engines such as those used in diesel powered vehicles are typically ignited by a mixture of injected fuel and hot compressed air. While diesel engines provide higher thermal efficiency than spark-ignited gasoline engines, for instance, diesel engines are known to emit undesirable exhaust emissions, such as high levels of nitrogen oxide (NOx) and black particulate smoke, which are undesirable. Thus, government agencies require diesel engines to meet strict regulations regarding the quantity of exhaust emissions in an effort to reduce pollutants in the environment. The environmental emissions regulations for these engines are becoming more stringent and difficult to meet, particularly for emissions resulting from fossil fuel combustion.
There is a need to monitor and control the combustion process, not only to reduce engine-out emissions, but also to produce the exhaust gas composition and temperature necessary to enhance the operation of after treatment-devices used to reduce emissions.